Process of cleaning xerographic plates



Dec. 9, 1969 D. ENSMlN-GER 3,433,034

PROCESS OF CLEANING. XEROGRAPHIG PLATES Filed Dec. 50, 1964 POWER SUPPLY I INVENTOR.

DALE ENSMINGER ATTORNEYS United States Patent i U.S. Cl. 134-1 3 Claims ABSTRACT OF THE DISCLOSURE Method and apparatus for cleaning residual powder particles from the surface of a xerographic plate in which the surface to be cleaned is submerged in a liquid medium and subjected to a source of sonic energy therein. Vibrations are induced into the liquid medium by the source of sonic energy to produce at the plate surface a turbulent scrubbing action to remove the powder particles. The intensity of the vibrations are controlled to produce a cavitation of the liquid about the plate surface and form a vapor cushion of the liquid medium therein to moderate the turbulent scrubbing action and prevent chipping, cracking, peeling or other adverse effects to the Xerographic plate.

This invention relates to xerography and in particular, to improved process for removing residual developer powder from xerographic plates.

The process of xerography, as disclosed in Carlson Patent No. 2,297,691, issued Oct. 6, 1942, employs a xerographic plate comprising a layer of photoconductive insulating material, on a conductive backing which is given a uniform electric charge over its surface and is then exposed to a subject to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the radiation intensity that reaches them and thereby creates an electrostatic latent image on or in thephotoconductive layer. Development of the latent image is effected with an electrostatically charged, finely divided material such as an electroscopic powder which is brought into surface contact with the photoconductive layer and is retained thereon electrostatically in a pattern corresponding to the latent electrostatic image. Thereafter, the developed xerographic powder image is usually transferred to a support means to which it may be fixed by any suitable means. Characteristic of the transfer step, as will be explained below is that most, but not all the powder transfers such that a residual image of tenaciously clinging powder remains on the xerographic plate and which must be cleaned off before recycling the plate for subsequent use.

Currently marketed xerographic machines perform the above process in cyclic fashion using a xerographic plate usually in the form of a rotating drum comprising about a 50 micron layer of vitreous selenium coated on an aluminum substrate. In these machines and others, the cyclic steps are continuously performed such that the rate of cleaning must be compatible with the other steps in order not to impose limitations on the speed of the system. In this continuous type operation, therefore, it is necessary that the drum be restored to its original clean condition after each powder transfer and before being recharged and carried through the recycle to produce subsequent copy. Because selenium is relatively soft and easily abraded, the cleaning mechanism must be inherently characterized by not deleteriously affecting the sensitive photoconductive surface.

It has been known in the art that brushes, cotton webs or other cleaning means generally of suitable soft, natural or synthetic materials supported in relative moving direct contact with the drum, when preceded by an electroice static discharge to neutralize the powder retaining forces, are generally effective to remove the residual developer powder. This type of cleaning apparatus, while widely used has commonly required a greater frequency of maintenance than has otherwise been necessary for the remaining components of the copying apparatus. Natural Australian rabbit pelt, because of its softness, bristle length and triboelectric properties has been the predominant material used for brushes. However, as should be appreciated, any natural fur is inherently expensive because of limited availability, processing costs and other factors. At the same time, mechanical movement and centrifugal forces associated with these prior type devices is known to dislodge powder from the cleaning surface creating an undesirable dust condition in and about the xerographic apparatus.

Various other techniques have been tried in order to overcome the disadvantages associated with brush and web cleaning system. These have included attemptswith the use of sonic and ultrasonic energy and which proved completely unsuccessful. Instead of cleaning the plate as intended the emitted energy was found to cause cracking, chipping and removal of the selenium from its substrate destroying the delicate plate to a degree whereby sonic and ultrasonic techniques were regarded as more suitable as a means for removing selenium from used plates.

Now in accordance with the present invention there has been discovered process, whereby residual developer powder remaining on the xerographic plate after image transfer can be effectively removed without the attendant handicaps that were heretofore known in the art.

These problems encountered in prior art devices are overcome in accordance with the invention by which a plate surface after transfer is contacted with a fluid medium having controlled properties appropriately selected as will be described and through which energy in the sonic to ultrasonic range is transmitted directionally toward the surface to be cleaned. The degree of cleaning is highly effective and is achieved without adversely affecting the selenium photoconductor. The removed developer may then be carried from the cleaning zone by the fluid material or by other removal means.

Thus, it is an object of the invention to provide novel method to effectively clean residual developer powder from xerographic plates without deleteriously affecting the delicate photoconductive surface thereof.

A further object of the invention is to provide novel method for cleaning xerographic plates of residual images without the ambient dust condition as was heretofore known. in the art.

For abetter understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description of the invention to be read in connection with the drawings wherein:

FIG. 1 is a schematic illustration of a typical Xerographic machine incorporating the improved cleaning apparatus of the invention.

FIG. 2 is an enlarged sectional view illustrating a preferred embodiment of the improved plate cleaning device.

For a general understanding of the xerographic processing system in which the invention is incorporated, reference is had to FIG. 1 in which the various system components are schematically illustrated. As in all xerographic systems based on the concept disclosed in the above-cited Carlson patent, a radiation image of copy to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged developing material to form a xerographic powder image corresponding to the latent image on the plate surface. The powder image is then electrostatically transferred to a support surface to which it may be fixed by a fusing device whereby the powder image is caused permanently to adhere to the support surface.

In the illustrated xerographic apparatus original copy to be reproduced is placed on a support tray from which it is fed onto a feed apparatus generally designated 11. On the feed apparatus, an original is placed on an endless belt 12, driven by motor 13 to pass the optical axis of projection lens system 14 that is illuminated by projection lamp LMP1. The image of the original is reflected by a mirror 15 through an adjustable objective lens 16 and then reflected by mirror 17 downwardly through a variable slit aperture assembly 18 and onto the surface of a xerographic plate in the form of a drum 19.

Xerographic drum 19 includes a cylindrical member mounted in suitable bearings in the frame of the machine and is driven in a clockwise direction by a motor 24 at a constant rate that is proportional to the transport rate of the original, whereby the peripheral rate of the drum surface is identical to the rate of movement of the projected radiation image. The drum comprises a layer of photoconductive material on a conductive backing that is sensitized prior to exposure by means of screened corona generating device 25, which may be an adaptation of the type disclosed in Vyverberg patent US. 2,836,725 that is energized from a suitable high potential source.

The exposure of the drum to the radiation image discharges the photoconductive layer in the area struck by radiation, whereby there remains on the drum a latent electrostatic image in image configuration corresponding to the radiation image projected from the original. As the drum surface continues its movement, the latent electrostatic image passes through a developing station 26 whereat an endles donor belt 27 loaded with developer particles passes around roll 28, into and out of contact with the surface of drum 19.

Before arriving at developing station 26, the belt, being driven by motor 33 connected to guide roll 29, receives a thin uniformly distributed layer of electroscopic marking particles 36 which have been dusted or loaded on the donor belt by means of loading apparatus 35. In the loading apparatus 35, developer material 38 is cartied up by a conveyor 39, driven by suitable drive means from motor 40, and then released onto chute 41 wherefrom it cascades down over the belt. The developer material may conveniently be a two-component mix of toner 36 and carrier beads of the general composition and nature described in Walkup Patent Nos. 2,618,551 and 2,638,416. As the developer material 38 is cascaded over the belt, a quantity of the toner component particles of the developer mix 38 is dusted and deposited uniformly on the surface thereof while the remainder is returned to the bottom of the loading apparatus 35. The toner component 36, that is consumed in dusting and subsequently in developing, is stored in dispenser 46 and is dispensed in amounts controlled by gate 47. The dusted donor belt then passes over guide roller and past an optionally required corona charging device 74 which applies additional charge to the dusted toner in order to facilitate the selective transfer of the toner to the image pattern on the drum.

Afer developing, the Xerographic powder image passes a discharge station 50 at which the drum surface is illuminated by lamp LMP-2 whereby residual images on the non-image areas of the drum surface are completely discharged. Thereafter, the powder image passes through an image transfer station 51 at which the powder image is electrostatically transferred to a moving support surface 52 by means of second corona generating device 53 similar to corona charging device 25, mentioned above.

The moving support surface 52 to which the powder image is transferred may be of any convenient type, such as paper, and may be obtained from a supply roll 56, fed over guide roll 57 and over suitable tensioning rolls being directed into surface contact with the drum in the immediate vicinity of transfer corona generating device 53. After transfer, the support surface 52 is separated from the drum surface and guided through a fusing apparatus 58 wherein the powder image is permanently affixed thereto. Thereafter, the support surface may be fed over a further system of guide and tensioning rolls, of which roll 59 is one, and onto a take-up roll 60 that is driven through suitable drive means by motor 61.

After separation of the support surface 52 from the drum, a corona generating device 64 may be employed to direct electrostatic charge to the residual powder image on the drum surface. This is regarded as unnecessary when utilizing energy transmitting liquids in the subsequent cleaning step which are relatively electrically conductive. Thereafter, the xerographic drum surface passes through a cleaning station 65 whereas a selective fluid 75, as will be described is contained in tank 81 in an energized condition and contacts the drum surface as it rotates past, whereby residual developing material remaining on the drum surface is removed. The drum surface may then pass through a second discharge station 68 at which it is illuminated by a fluorescent lamp LMP-3, whereby the drum surface in this region is completely flooded with light to remove any electrostatic charge that may remain thereon. This is likewise regarded as unnecessary when utilizing an energy transmitting liquid that is relatively electrically conductive. Suitable light traps are provided in the system to prevent any light rays from reaching the drum surface, other than the projected image, during the period of drum travel immediately prior to sensitization by corona generating device 25 until after the drum surface is completely passed through the developing station 26.

Refer now also to FIG. 2 wherein an embodiment of improved apparatus is shown performing the cleaning process of the invention. To effect cleaning at cleaning station 65, there is provided a tank or reservoir 81 in which is contained liquid 75. Supported within the liquid is a transducer unit 79, adapted to emit sonic or ultrasonic energy and connected to an outside power source 77 by wires 89 through sealed openings 90 in the tank.

The transducer 79 which may be an appropriately adapted commercially marketed unit is comprised herein of a piezoelectric device about one inch in width comprised of zirconate-lead titanate (polarized), barium titanate, or its equivalent supported the drum length parallel spaced about /4 inch from the drum surface. This w'idth will, of course, vary with drum speeds to permit adequate exposure to the sonic or ultrasonic energy unit as the drum passes through the cleaning zone.

The sonic or ultrasonic energy, when selectively transmitted via the liquid, is capable of removing the residual developer from the selenium surface without removing the selenium per se from its substrate. In order to render the invention operable with vitreous selenium as the photoconductor, it has been found that the liquid 75 should be characterized by a boiling point generally in the range of F. F. with a heat of vaporization less than that of water, and which liquid is preferably, although not necessarily also a non-solvent of the resin toner 36. Non-solvents have been found to facilitate removal of the residual powder image. It also permits recycling the liquid after use by merely passing it through a filter. The latter would not readily be feasible if the toner dissolved in the liquid.

Byway of example, 1,1,l-trichloro-pentafiuoropropane (Freon 215), or a 50-50 mixture, by volume, of methyl alcohol (MEOH) and water are typical liquids which have the selective combination of physical properties enumerated above. Other liquids will readily occur to those skilled in the art and with other photoconductors these requirements may or may not pertain.

The liquid is subjected to energy emission by the transducer operating in the sonic to ultrasonic frequency range.

In the ultrasonic ranges of about 18 to 1,000 kilocycles per second the transducer transmits the energy through the liquid into contact with the selenium drum surface. Because of the high vapor pressure, the liquid is caused by the emitted energy to cavitate at an intensity level below that which will damage the selenium but above that which will provide an effective scrubbing action on the selenium surface and form a cushioning layer of vapor bubbles 85 along the selenium surface. This, it is believed, cushions the turbulence of the ultrasonic field intensity at the selenium surface to a regulated degree whereby to dislodge the residual powder image while not chipping, cracking, removing, or otherwise deleteriously affecting the selenium per se.

Subjecting the liquid to energy emission by the transducer operating generally in the sonic range of about 60 cycles to 18 kilocycles per second is likewise effective in accordance herewith although requiring a longer operating time than when operating in the aforesaid ultrasonic ranges. This lower frequency at slightly greater amplitude of excitation likewise causes the liquid to cavitate and form a cushioning layer of vapor bubbles whereby to effectively remove the residual powder image while not deleteriously effecting the selenium.

By varying the shape, size, amplitude and frequency of oscillation of the transducer 79, the necessary time of plate exposure to energized liquid can be controlled within limits. Likewise, the impingement direction of the energy wave oscillation components to the plate surface, as well as the physical properties of the transmitting liquid will influence the energy intensity at the surface and can be controlled to effect subsantially complete removal of the residual image. These variables may be selectively chosen and combined to satisfy individual copying or manufacturing requirements. By operating the transducer to energize one of the above-named or other liquids to or slightly above the onset of cavitation such that the impingement direction of the energy wave oscillation components are essentially normal to the drum surface with the drum surface immersed in the liquid to a depth of about two inches for about seconds, it was found that substantially complete removal of the residual image was achieved.

To maintain the liquid reusable for continuous operation pump 91, operated through suitable drive means by motor 92, slowly circulates the liquid from tank 81 through drain pipe 93 to a settling or filter tank 94 wherein the removed toner is extracted and then returned to the tank in a clean condition. The settled toner in the tank 94 may be removed periodically as required.

Although the two above-named liquids have been found suitable for toner removal by the use of sonic or ultrasonic energy, as above-described, it is apparent that other liquids with physical properties similar to those described above may also be used. It should also be apparent that with different resin toners and xerographic plates, other liquids and fluids may be successfully used to clean xerographic plates by the process and apparatus described herein.

By the above description, there is disclosed novel process for cleaning a xerographic plate with sonic or ultrasonic energy through a fluid media to effect removal of residual developer powder from the plate. The process, is relatively cleaner than that performed by cleaning apparatus used in presently available copying machines.

What is claimed is: 1. A method for cleaning residual powder particles from the photoconductive surface of a xerographic plate comprising,

submerging the surface of said xerographic plate with residual powder particles thereon in a liquid medium characterized by having a boiling point ranging from about F. to about F.

subjecting the submerged surface of said xerographic plate to a potential source of ultrasonic vibrations within said liquid medium,

energizing said source at a predetermined intensity level to induce vibrations within said liquid medium, said induced vibrations being at an energy level above that which produces a turbulent scrubbing action on said plate surface but below that which adversely affects said plate surface, said induced vibrations further being of sufficient magnitude to produce a cavitation of said liquid medium about said plate surface and generate a vapor of said liquid between the plate surface and said liquid medium, said source of ultrasonic vibrations being spaced from the plate surface a predetermined distance so that said generated vapor forms a cushion adjacent said plate surface to moderate the turbulent scrubbing action of said liquid medium on said plate surface, and maintaining said source energized over a predetermined time period, said predetermined time period being of a duraton suflicient for the moderated scrubbing action of said liquid medium to remove said powder particles from said plate surface but of insufiicient duration to adversely affect said plate surface.

2. The method according to claim 1, said liquid medium comprising a 50-50 mixture, by volume, of methyl alcohol and water.

3. The method according to claim 1, said liquid medium comprising 1,1,1-trichloropentafiuoropropane.

References Cited UNITED STATES PATENTS 2,967,119 1/1961 Gutterman 15100 3,099,584 7/1963 Walsh 1341 3,128,683 4/1964 Rubin 1341 X 3,158,886 12/1964 Grimes 15-10O 3,186,838 6/1965 Gratf et a1. 15-100 SAMIH N. ZAHARNA, Primary Examiner 

